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We present a direct observation of carbon-atom tunneling in the flipping reaction of formaldehyde between its two mirror-reflected states on a Cu(110) surface using low-temperature scanning tunneling microscopy (STM). The flipping reaction was monitored in real time, and the reaction rate was found to be temperature independent below 10 K. This indicates that this reaction is governed by quantum mechanical tunneling, albeit involving a substantial motion of the carbon atom (∼1 Å). In addition, deuteration of the formaldehyde molecule resulted in a significant kinetic isotope effect (RCH2O/RCD2O ≈ 10). The adsorption structure, reaction pathway, and tunneling probability were examined by density functional theory calculations, which corroborate the experimental observations.

Hydration layers play a key role in many technical and biological systems, but our understanding of these structures remains very limited. Here, we investigate the molecular processes driving hydration of a chiral metal-organic surface, bitartrate on Cu(110), which consists of hydrogen-bonded bitartrate rows separated by exposed Cu. Initially water decorates the metal channels, hydrogen bonding to the exposed O ligands that bind bitartrate to Cu, but does not wet the bitartrate rows. At higher temperature, water inserts into the structure, breaks the existing intermolecular hydrogen bonds, and changes the adsorption site and footprint. Calculations show this process is driven by the creation of stable adsorption sites between the carboxylate ligands, to allow hydration of O-Cu ligands within the interior of the structure. This work suggests that hydration of polar metal-adsorbate ligands will be a dominant factor in many systems during surface hydration or self-assembly from solution.

Highly corrugated, stepped surfaces present regular 1D arrays of binding sites, creating a complex, heterogeneous environment to water. Rather than decorating the hydrophilic step sites to form 1D chains, water on stepped Cu(511) forms an extended 2D network that binds strongly to the steps but bridges across the intervening hydrophobic Cu(100) terraces. The hydrogen-bonded network contains pentamer, hexamer, and octomer water rings that leave a third of the stable Cu step sites unoccupied in order to bind water H down close to the step dipole and complete three hydrogen bonds per molecule.

After growth of graphene by chemical vapour deposition on copper foil, Cu(4 1 0) facets were distinguished from Cu(1 0 0) facets using the low energy electron diffraction technique. Evolution of the diffraction patterns was studied after oxidation of the Cu substrate and subsequent annealing in ultrahigh vacuum. An ordered Cu(4 1 0)–O phase was then identified. The distinction between Cu(4 1 0) and Cu(4 1 0)–O is relevant in determination of the coupling between graphene and the substrate.

Significant changes in the Raman spectrum of single-layer graphene grown on a copper film were observed after the spontaneous oxidation of the underlying substrate that occurred under ambient conditions. The frequencies of the graphene G and 2D Raman modes were found to undergo red shifts, while the intensities of the two bands change by more than an order of magnitude. To understand the origin of these effects, we further characterized the samples by scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and atomic force microscopy (AFM). The oxidation of the substrate produced an appreciable corrugation in the substrate without disrupting the crystalline order of the graphene overlayer and/or changing the carrier doping level. We explain the red shifts of the Raman frequencies in terms of tensile strain induced by corrugation of the graphene layer. The changes in Raman intensity with oxidation arise from the influence of the thin cuprous oxide film on the efficiency of light coupling with the graphene layer in the Raman scattering process.

Dissociation of molecular oxygen is an important elementary process in heterogeneous catalysis. Here, we report on a real-space observation of oxygen photolysis on the Ag(110) surface at 78 K by far- and near-field excitation in the ultraviolet–near-infrared range using a low-temperature scanning tunneling microscope (STM) combined with wavelength-tunable laser excitation. The photolysis of isolated oxygen molecules on the surface occurs even by visible light with the cross section of ∼10−19 cm2. Time-dependent density functional theory calculations reveal optical absorption of the hybridized O2–Ag(110) complex in the visible and the near-infrared range which is associated with the oxygen photolysis. We suggest that the photolysis mechanism involves a direct charge transfer process. We also demonstrate that the photolysis can be largely enhanced in plasmonic STM junctions, and the cross section is estimated to be ∼10−17 cm-2in the visible and the near-infrared range, which appears to be an interesting feature of plasmon-induced reactions from the perspective of photochemical conversion with the aid of solar energy.

Agriculture in Taiwan is input-intensive. Chemical fertilizers are heavily used, and most arable land contains less than 2% of soil organic matter (SOM). To improve soil quality, to make agriculture sustainable, and to avoid over-production of rice, paddy rice–upland rotation and application of organic substances have been widely promoted. A change in the system often begins to alter the SOM content which takes from several up to even a hundred years to stabilize into a new SOM level. The purpose of this study was to find methods of determining long-term changes in SOM based on short-term data and to evaluate the effects of different kinds of organic materials in paddy–upland rotation. Organic matter was supplied as green manure, compost, and peat at similar intensity. SOM data were collected from the 1st to the 13th year for the calibration and validation of the model that was intentionally assembled for less mechanisms yet research purpose achievable. The ratio of the quantity of organic matter applied to that retained in soil was the lowest when organic C was supplied by growing green manure and the highest, or 3.7 times the control plot, when it was supplied in the form of compost. The minimum period for which data of SOM was required to calibrate the model varied with the form of organic matter: 5 years for green manure, 6 years for compost or peat, and 7 years for the control. The minimum years of data required for reliable calibration were significantly related to the return amounts of crop residues (R2 = 0.807). In each application strategy, SOM contents in the 12th and 13th years were validated well with those predicted by the calibrated model. Relative sensitivity analysis showed that soil temperature and water are the two major factors that affected SOM content; while the humus-like portion of organic matter determined the potential to accumulate SOM. Long-term simulations suggested that it might take at least 20 years for SOM in these fields to be stabilized.

The organic carbon in highly variable dye wastewater could be decomposed by microorganisms. The carbon turnover had some similarity to the transformation of soil organic matter, in that both systems had complicated carbons in the initial, intermediate and final phases, with microorganisms activating the decomposition. These processes could be simulated using a dynamic model that includes a system of differential equations representing six state variables, namely the liable decomposable fraction (LDF), the resistant decomposable fraction (RDF), active biomass (BAC), inactive biomass (BIA), decomposable (DOM) and non-decomposable organic materials (NDM). The relationship between these variables and traditional wastewater properties, e.g. chemical oxygen demand (COD) and biological oxygen demand (BOD), was defined in the context of experimental data acquisition and model evaluation. The model was calibrated by simulating several conditions, such as increasing the organic loading and hydraulic retention time (HRT), varying the C/N ratio of the organic substances in the dye wastewater and changing the treatment temperature. With the data from these experiments, a set of parameters related to the transformation rate and proportion was identified to represent the results from each experiment. This fitting allowed the model to be useful in carrying out more simulations for characterizing the efficiency of different treatment strategies. The results showed that in order to meet discharge COD regulations

Ordered configurations of hydrogen adatoms on graphene have long been proposed, calculated, and searched for. Here, we report direct observation of several ordered configurations of H adatoms on graphene by scanning tunneling microscopy. On the top side of the graphene plane, H atoms in the configurations appear to stick to carbon atoms in the same sublattice. Scanning tunneling spectroscopy measurements revealed a substantial gap in the local density of states in H-contained regions as well as in-gap states below the conduction band due to the incompleteness of H ordering. These findings can be well explained by density functional theory calculations based on double-sided H configurations. In addition, factors that may influence H ordering are discussed.

Few-layer graphene grown on Ni thin films has been studied by scanning tunneling microscopy. In most areas on the surfaces, moire patterns resulted from rotational stacking faults were observed. At a bias lower than 200 mV, only one sublattice shows up in regions without moire patterns while both sublattices are seen in regions with moire pattens. This phenomenon can be used to identify AB stacked regions. The scattering characteristics at various types of step edges are different from those of monolayer graphene edges, either armchair or zigzag.